1. Field of the Invention
The subject invention relates to memory circuitry and more particularly to a control circuit for controlling memory write logic and output states during disconnection of the memory from a plug-in power source.
2. Description of Related Art
In the prior art, circuitry for maintaining memory integrity in the face of power down procedures or power outages is known. Such circuitry typically employs power supply detect circuits or voltage comparators, which draw relatively large currents and consume relatively large amounts of power. Such circuitry also must have access to battery voltage to operate during power-up, power-down and battery hold time i.e. standby conditions. It is also not specifically designed for use in an environment where a memory is supplied with power through a plug-in connection which may be randomly disconnected.
The prior art circuitry is also relatively complex, employing, for example, flip-flop circuitry and/or operational amplifiers. In the case of CMOS operational amplifier circuitry, the circuitry ceases to function below 1.5 volts. Operation below this voltage level has appeared desisrable to the inventor.
Thus, the prior art has not provided a number of capabilities which have appeared advantageous. The prior art has not provided a power down logic control circuit operable at very low voltages and which draws little or no current during battery hold time. The prior art has lacked a power down logic control circuit which will prevent memory loss and ensure proper control of logic levels when used in conjunction with a memory module which is subject to being disconnected at random times from the normal power supply without any prior power-down procedures. In particular, a low voltage power down circuit has not been available which will control logic levels and the transition to standby battery power where a plug-in memory module is randomly and manually pulled out of a plug-in power connection. Power down logic control circuitry which does not require access to battery voltage during power down and standby conditions also has not been available.